[Zope] Zope Versions unusable?

[Jim Fulton]

Jochen Haeberle wrote:
> 
> Hi,
> 
> I had to discard a version I was working on in Zope 2.1 twice already
> because in the normal view there happened a "VersionLockError":
> 
> Error Type: VersionLockError
> Error Value: ("'\\000\\000\\000\\000\\000\\000\\005\\341'", 'ArtikelVersion')
> 
> Traceback (innermost last):
>    File /serve/Zope-2.1.0-NR/lib/python/ZPublisher/Publish.py, line
> 214, in publish_module
>    File /serve/Zope-2.1.0-NR/lib/python/ZPublisher/Publish.py, line
> 179, in publish
>    File /serve/Zope-2.1.0-NR/lib/python/Zope/__init__.py, line 202, in
> zpublisher_exception_hook
>      (Object: ApplicationDefaultPermissions)
>    File /serve/Zope-2.1.0-NR/lib/python/ZPublisher/Publish.py, line
> 169, in publish
>    File /serve/Zope-2.1.0-NR/lib/python/ZODB/Transaction.py, line 237, in commit
>    File /serve/Zope-2.1.0-NR/lib/python/ZODB/Connection.py, line 327, in commit
>      (Info: (('*/z19MlDlV7e7P0QHV0lJ5A==', 'AdBanner'),
> '\000\000\000\000\000\000\005\341', ''))
>    File /serve/Zope-2.1.0-NR/lib/python/ZODB/FileStorage.py, line 614, in store
>      (Object: /serve/Zope-2.1.0-NR/var/Data.fs)
> VersionLockError: (see above)

Hm.  You should have gotten a more informative error message
that said something alomg the line of "this request could not 
be completed because it modified an object that has been modified in
a version".

> Is this something known to you?

Yes.

> Is this a bug?

No (except for the error message).

> Does anyone know when
> this can happen?

Yes. It happens when you try to modify an an object
that has been modified in (another) version. When you
modify an object in a version, the object is locked and
can only be modified in that version.  The effect of a change
can be wideer than expected. For example, adding an object 
to a folder modifies the folder.  If changing an
object causes a catalog to be updated, then changing
an object in a version locks the catalog, as well as
the object.


> Are there things to avoid when working in a version?

Avoid changing objects you don't want to lock.
 
> If this happens rather often and unknown to the content manager, I
> guess the Versions of Zope are rather unusable, because they do not
> protect your working securly!

Perhaps.  This is a function of the objects you are working with,
Objects that make far flung changes (e.g. objects that modify a 
central catalog) or objects that make changes in non-management
situtations don't work well with versions.  Perhaps objects 
that behave this way should provide some sort of warning when used 
in a version.

Jim

--
Jim Fulton           mailto:jim@digicool.com
Technical Director   (888) 344-4332              Python Powered!
Digital Creations    http://www.digicool.com     http://www.python.org

Under US Code Title 47, Sec.227(b)(1)(C), Sec.227(a)(2)(B) This email
address may not be added to any commercial mail list with out my
permission.  Violation of my privacy with advertising or SPAM will
result in a suit for a MINIMUM of $500 damages/incident, $1500 for
repeats.